The overall goal of this project is to test the efficacy of newly developed small, nonpeptide, gonadotropin-releasing hormone (GnRH) antagonists in suppressing reproductive hormone secretion in primates. Compounds are being administered to adult male rhesus monkeys, and blood samples collected to assess the effects on LH and testosterone levels. Development of effective compounds will provide new tools for suppressing reproductive hormone secretion for contraceptive purposes, control of reproductive hormone secretion in various cancers, and will also provide new tools for examining the effects of GnRH in the central nervous system.